1. Field of the Invention
The present invention relates to an apparatus and method for perforating well casing and/or a subterranean formation. More particularly, the present invention relates to an apparatus and process wherein a propellant is conveyed into a well within a shaped charge.
2. Description of the Related Art
Hydrocarbon producing wells typically include a casing string positioned within a well bore that intersects a subterranean oil or gas deposit. The casing string increases the integrity of the well bore and provides a path for producing fluids to the surface. Conventionally, the casing is cemented to the well bore face and subsequently perforated by detonating shaped explosive charges. These perforations extend through the casing and cement a short distance into the formation. In certain instances, it is desirable to conduct such perforating operations with the pressure in the well being overbalanced with respect to the formation pressure. Under certain overbalanced conditions, the well pressure exceeds the pressure at which the formation will fracture, and therefore, hydraulic fracturing occurs in the vicinity of the perforations. As an example, the perforations may penetrate several inches into the formation, and the fracture network may extend several feet into the formation. Thus, an enlarged conduit can be created for fluid flow between the formation and the well, and well productivity may be significantly increased by deliberately inducing fractures at the perforations.
Techniques for perforating and fracturing a formation surrounding a borehole are known in the art. The common technique of hydraulically pressurizing the borehole to expand or propagate the fractures initiated by the projectile can be expensive due to the preparation required for pressurizing a portion of a borehole. Typically, pressure around a production zone in the borehole is increased by pumping fluids into that portion of the well to obtain the high pressures necessary to expand the fracture in the production zones. This operation is generally time intensive and costly making these techniques unattractive for either multiple zone wells or wells with a low rate of production.
Gas generating propellants have been used in place of hydraulic fracturing techniques to create and propagate fractures in a subterranean formation. In one conventional arrangement, a perforating gun having shaped charges is fitted with a propellant charge and conveyed into the well. This propellant charge may be formed as a sleeve that surrounds a charge tube in which the shaped charges are secured. As is known, flammable or combustible material such as propellants require careful handling during all aspects of manufacture, transportation and deployment. Thus, protective measures are taken throughout all these phases to prevent unintended detonation of the propellant.
Thus, it is one object of this invention to provide methods and systems for safely and efficiently fracturing a well, particularly in connection with a perforation activity. Still other objects will become apparent below.